Product Code: ICAL08_101

Morphological and Thermal Modelling of Direct Metal Deposition: Application to Aeronautical Alloys
Authors:
Patrice Peyre, Lalp-Gerailp, Upr 1578 Cnrs; Arcueil France
Pascal Aubry, Gip-Gerailp; Arcueil France
Ry Fabbro, Lalp-Gerailp, Upr 1578 Cnrs; Arcueil France
Presented at ICALEO 2008

Direct metal deposition (DMD) allows to generate complex structures from the interaction between a projected powder and a laser beam, with or without using a coaxial device. One of the main issues to address concerns the prediction of layer widths and heights from the laser and powder parameters, in order to allow thermal or thermo-mechanical modelling in a second step. Indeed, most of the thermal or thermo-mechanical simulations of DMD considered a-priori wall geometries, which strongly limits their predictive aspect. For this purpose, a simplified finite element-aided analytical modelling was developed and successfully tested on two aeronautical materials : Ti6Al4V titanium alloy and Inconel 718 Nickel-based superalloy.
Our analytical model first considered on a spatially discretized surface the local interaction between the FE simulated melt-pool (in steady state condition) and the local powder feed rate Dm (g/min) distribution, then provided us with average values for the to layers widths wi and heights Dhi on growing wall-like structures. By an incremental approach, this allowed us to predict the entire geometry of a growing wall on a substrate, considering separately each manufactured layer. A thermal limitation to layer growth was also implemented in the model to address specific conditions for which thermal energy contained into the melt-pool does not melt all the incident powder. A comparison with experimental data was shown to be satisfactory on a large range of experimental conditions. In a second step, rather simple thermal simulations carried out on COMSOLTM FE software, and using a specific function for the thermal conductivity k (t,T,x,z) to address additive layers, allowed to reproduce with a good accuracy thermal cycles and melt pool dimensions during the construction of Ti6Al4V walls. This was confirmed by comparisons between numerical simulations and experimental T=f(t), and by fast camera recordings of melt pools. It was concluded that our dual simulation-aided morphological + thermal model is a rather efficient and novel method for predicting geometries and heat cycling of manufactured walls.